The present invention relates to a guided beam type of flat display device wherein at least one and preferably each of a plurality of electron beams are scanned over a different area portion of an image screen.
One structure which has been proposed for a large area screen flat display device comprises a thin box-like envelope with one of the large sides thereof constituting a faceplace on which a phosphor screen is disposed. Within the envelope are a plurality of spaced, parallel support (against external atomospheric pressure) walls perpendicularly disposed to and between the large sides of the envelope thereby forming a plurality of parallel channels. Across one end of the channels is a gun structure which directs at least one electron beam along each of the channels. In each of the channels is a beam guide which confines the electron beam in the channels and guides the beam along the length of the channel. The beam guide also includes means for deflecting the electron beam out of the beam guide at selected points along the beam guide. The beams in all of the channels are preferably simultaneously deflected out of their beam guides toward the phosphor screen at each of the selected points.
Along the support walls at each side of each channel are deflection electrodes whereby each beam in each channel can be deflected transversely across the channel to achieve a line-by-line scanning of a portion of the phosphor screen. As the beams are deflected transversely across their respective channels, the beams are modulated to provide a desired display on the phosphor screen. A display of this type is described in the application for U.S. Letters Patent of C. H. Anderson, et al., Ser. No. 615,353 filed Sept. 22, 1975, now U.S. Pat. No. 4,028,582, issued June 7, 1977, entitled "Guided Beam Flat Display Device".
A problem in this type of display device is to be sure that each beam is in the proper position when it is modulated with the desired information. If any beam overscans its channel while it is being modulated, some of its contribution to the overall display is lost. Conversely, if a beam underscans its channel, blank spots will occur in the display. Therefore, it would be desirable to provide means for controlling the modulation of the beams with respect to the position of the beams to achieve a satisfactory display.